An error compensation technique for ensuring reliability of communication includes a forward error correction (FEC) scheme and an automatic repeat request (ARQ) scheme. In the FEC scheme, an error at a reception end is corrected by adding an extra error correction code to information bits. In the ARQ scheme, an error is corrected through data retransmission, for which there are a stop and wait (SAW) scheme, a go-back-N (GBN) scheme, a selective repeat (SR) scheme, and the like. The SAW scheme is a scheme in which whether or not a transmitted frame has been properly received is checked and then a next frame is transmitted. The GBN scheme is a scheme in which N number of successive frames are transmitted, and if a successful transmission is not made, every transmitted frame subsequent to an error-generated frame is retransmitted. The SR scheme is a scheme in which only an error-generated frame is selectively re-transmitted.
The FEC scheme is advantageous in that a time delay is small and there is no need to transmit and receive information between a transmission end and a reception end, but a system efficiency is degraded in a good channel environment. The ARQ scheme has a high transmission reliability but is disadvantageous in that a time delay occurs and a system efficiency is degraded in a poor channel environment. A hybrid automatic repeat request (HARQ) scheme combining the FEC and ARQ has been proposed to resolve such shortcomings. According to the HARQ scheme, whether or not data received by a physical layer has an error that cannot be decoded is checked, and if the data has an error, retransmission of data is requested to thus enhance performance.
The receiver of the HARQ scheme basically attempts an error correction on received data and determines whether or not data retransmission is required by using an error detection code. As the error detection code, a cyclic redundancy check (CRC) may be used. When an error of reception data is detected through the CRC detection process, the receiver transmits the NACK signal to the transmitter. Upon receiving the NACK signal, the transmitter transmits proper retransmission data according to the HARQ mode. Upon receiving the retransmission data, the receiver combines the previous data and the retransmission data and decodes the same to thereby improve reception performance.
The retransmission scheme of the HARQ may be classified into a synchronous scheme and an asynchronous scheme. In the synchronous HARQ, data is retransmitted at a point of time both the transmitter and the receiver knows about, so signaling required for transmission of data such as an HARQ processor number or the like can be reduced. In the asynchronous HARQ, resources are allocated at an arbitrary time for retransmission. The asynchronous HARQ provides flexibility of resource allocation.
Meanwhile, the wireless communication system may include a relay station (RS) in addition to a base station (BS) and a mobile terminal (MS). The RS serves to extend a cell coverage and improve a transmission performance. When the BS provides a service to an MS located outside the coverage of the BS via the RS, the RS may relay both control signals and data signal between the corresponding MS and the BS, thus extending the cell coverage of the BS. In addition, when the BS provides a service to an MS located within the coverage of the BS via the RS, the RS may amplify a data signal between the BS and the MS and transfer the amplified signal to each reception end, to thereby improve a transmission performance. The presence of RS is required especially when an MS is in a shadow area within the coverage of the BS.
When the RS is disposed between the BS and the MS, performing HARQ is problematic. The reason is because HARQ generally considers only a one-to-one situation between the BS and the MS, so the presence of RS requires consideration of HARQ between the RS and the BS and HARQ between the RS and the MS. In particular, if the synchronous HARQ is performed between the BS and the MS in the conventional wireless communication system, how to perform HARQ of the RS without affecting the synchronous HARQ matters.